1. Field of Technology
The present invention relates to technology for detecting removal of conveyed work.
2. Description of Related Art
Paper, CD-ROM discs, and other printed media are examples of conveyed work as used below. Japanese Unexamined Patent Appl. Pub. 2000-20274 teaches a method of using a sensor for detecting print media (referred to below as a “print media sensor”) to measure the width of the print medium (the length of the transverse direction perpendicular to the transportation direction) in a printer. Japanese Unexamined Patent Appl. Pub. H06-19640 similarly teaches a method of using a print media sensor to detect if a print medium is present at a specific location in the print media transportation path of the printer.
Sometimes, however, the print medium is pulled out of the transportation path by force. A means of detecting if the print medium has been removed in this way at any point in the print media transportation path is therefore desirable. This can be done by, for example, using a plurality of these print media sensors located at intervals less than the length (in the direction in which the print media are conveyed) of the print media supported by the printer.
The internal arrangement of the printer, cost considerations, and other problems, however, mean that the above methods cannot always be used. A conventional printer of this type therefore usually cannot detect if the print medium has been removed from any point in the transportation path. The inability to detect if the print medium has been removed can result in problems such as described below.
(1) Printing proceeds on the assumption that the print medium is present, and the printing process thus ends as though the print data (text or image, for example) was actually printed even though the print data was not printed on the print medium.
(2) Because printing proceeds as though the print medium is present, the ink or other printing material is deposited on the transportation path. The platen can even be damaged in a dot impact printer as a result of the pins firing directly against the platen with no intervening paper.
The ability to detect in as many situations as possible if the work being conveyed has been removed during transportation is desirable regardless of the type of work being conveyed, and is not limited to print media.
A first embodiment of the invention described herein therefore enables detecting in as many situations as possible if an object being conveyed has been removed during transportation.
Other aspects and effects of the present invention will be known from the description of the invention following below.